Fluorescent lighting has been around for many years now. This form of lighting started out as a highly efficient alternative for incandescent light bulbs, but has recently been surpassed by LED lighting to some extent in terms of efficiency and power consumption, and also in other aspects as set out below.
Fluorescent lamps generally comprise a tube filled with an inert gas and a small amount of mercury, capped at both ends with double pinned end caps which fits in the connectors of the fixture.
For assisting the ignition of the fluorescent lamp the end caps of the fluorescent lamp contain a filament to preheat the gasses inside the tube and to vaporize the mercury. Once the fluorescent lamp is ignited, heat generated by the conducted current keeps the fluorescent lamp in operational condition. To facilitate these starting conditions and to limit current through the fluorescent lamp during operation, and thus limit the power consumed, a ballast is connected between the mains power supply and connectors of the fixture.
In installed fixtures for fluorescent lamps two different types of ballasts are used. A type of ballast which is already used since the introduction of fluorescent tube lamps is the so-called magnetic ballast. Such magnetic ballasts is a simple magnetic inductor, which limit consumed power by limiting the AC current as a result of the frequency dependent impedance of the inductor.
More recently electronic ballasts have been introduced. Such electronic ballasts usually first convert AC mains power into DC power, and subsequently convert the DC power into high frequency AC power to drive the fluorescent lamp.
Several different types of electronic ballasts are installed.
Nowadays retrofit LED lamps for replacing the conventional fluorescent tube lamps are available on the market.
US2015/0198290 discloses a low cost and efficient retrofit lamp which can be used in luminaries having a magnet ballast, but also in fixtures with an electronic ballast.
The ends of the retrofit LED lamp comprise connector pin pairs which fit in the connectors of the fixture.
Impedances are connected between the connector pin pairs. The AC current received via the connector pin pairs is rectified. The rectified current is supplied to LED circuitry comprising LEDs which emits light when energized by the rectified current.
When the retrofit lamp is energized via an magnetic ballast the frequency of the AC current supplied to the lamp is equal to the low frequency (50 or 60 Hz) of the mains voltage. The rectified current comprises an AC component with a frequency which is twice the frequency of the mains voltage. This AC component causes flickering in the emitted light. To reduce this flickering a flicker reduction circuit in the form of a capacitor is periodically connected and disconnected in parallel over the LED circuitry.
In contrary to a magnetic ballast, which all operates substantial in same way, there are many different types of electronic ballasts.
It appears that retrofit lamps provided with flicker reduction when used in combination with a magnetic ballast do not always correctly function in combination with some types of electronic ballasts.
Since the customer in general does not know which ballast is used in a fixture it is important that the can trust that a retrofit lamp will correctly function in his fixture, notwithstanding the type of ballast used in the fixture.